Lewandowsky says the study, which was conducted in 2003 during the closing phases of the war and soon afterwards, was triggered by the number of retractions that occurred in the media at the time.

"It struck us as remarkable how many things were reported and then subsequently corrected," he says.

The first part of their study looked at how people processed corrections that occurred in the early days of the war.

The researchers asked whether people believed statements based on two kinds of press reports: one type that had been retracted and one that continued to be reported as fact.

The four statements based on reports that participants knew had been retracted were:

* The allies captured an Iraqi general during the first one to two weeks of the war

* Allied POWs (Prisoners of War) were executed by the Iraqis after being captured and/or surrendering

* Toward the end of the first week of the war, there was a significant civilian uprising against the Iraqi Baath Party militia in Basra, and

* During the first few days of the war, an entire Iraqi division (some 8000 soldiers) was captured and/or surrendered to the allies.

"We tried to be as balanced as possible whether it put the Iraqis in a bad light, or the Coalition forces, to the extent that that was possible," Lewandowsky says.

Sceptics and non-sceptics

The researchers also classified people as sceptical if they disagreed with the official reason given for war, ridding Iraq of weapons of mass destruction (WMDs).

The results showed there were far fewer sceptics in the US than in Germany and Australia. And that such sceptics were less likely to believe statements that they knew had been retracted than those people classified as non-sceptical.

"The main finding about suspicion is confirming what we have known for quite a while from laboratory studies," says Lewandowsky.

"People do not discount corrected information unless they are suspicious about it or unless they are given some other hypothesis with which to interpret the information."

He says this has important implications in the judicial system where judges often instruct juries to disregard certain information.

"It turns out that jurors don't disregard information even if they are directed to do so unless they are being made suspicious about why the information was actually used in the first place. So, exactly what we found."

False memories

The study also supports certain theories about the formation of false memories, says Lewandowsky.

"The constant hinting at WMDs was sufficient to make some people believe that they have been found," he says.

Lewandowsky says the study confirmed previous findings that around 30% of US respondents say weapons of mass destruction have been found in Iraq since the war started.

By contrast, he says, only 17% of Australians and only 5% of Germans believe this was the case.

"Given that that is in fact not true, given that none has ever been discovered, we would classify those responses as a false memory," says Lewandowsky.

He can't explain why this is the case but thinks that scepticism may also play a role.

"Overall, our scientific understanding of human memory reveals it as a device that is prone to considerable error and distortion," says Lewandowsky, referring to other research on the ability of victims to remember perpetrators of a crime.

"Even when they are not being actively manipulated, there is consistent evidence that people often mistakenly identify 'perpetrators' from a line-up of entirely innocent people."